I'm running a Mellings HV pump with 15W-40 Shell Rotella oil on my SB (with a stock pan). I don't have pressure fluctuations, oil loss, oil consumption or any other oil problems. I've got 50 psi @idle and 75 psi at 3000 rpm (cruise). I'm also running one PCV valve. To suggest his problems are oil pump related is off-base. I'd suspect excessive blow-by from poor ring seating. If the motor was put together and machined correctly, then this thread wouldn't exist. Run a leak down check and confirm the obvious.